Field of the Invention
The present invention relates to an electrode assembly with improved stability and a method of manufacturing the same, and more particularly, to an electrode assembly with improved stability capable of decreasing shrinkage ratio of a separator and a method of manufacturing the same.
Description of the Related Art
Secondary batteries receive attention as a power source of an electric vehicle (EV), a hybrid electric vehicle (HEV), a parallel hybrid electric vehicle (PHEV), etc., suggested as a means for solving the air pollution of a common gasoline vehicle, a diesel vehicle, etc. using fossil fuel. In a medium and large size device such as a vehicle, high power and high capacity are necessary, and a medium and large size battery module in which a plurality of battery cells are electrically connected is used.
However, since the medium and large size battery module is preferably manufactured to have a small size and light weight, a prismatic type battery, a pouch type battery, etc. having high stacking degree and light weight with respect to capacity have been mainly manufactured as the battery cell of the medium and large size battery module.
In general, an electrode assembly is classified according to the structure of the electrode assembly having a cathode/separator/anode structure, and typically is classified into a jelly-roll type (roll type) electrode assembly having a rolled structure of long sheet type cathodes and anodes with a long sheet type separator disposed therebetween, and a stack-type (laminated type) electrode assembly obtained by stacking a plurality of cathodes and anodes cut into a certain size with a separator therebetween in sequence. Preferably, the structure of the electrode assembly includes a stack-type structure and a stack/folding type structure.
The stack type structure is widely known in the art, and the explanation thereon will be omitted in the present disclosure. Detailed description of an electrode assembly having the stack/folding type structure is disclosed in Korean Patent Application Publication Nos. 2001-0082058, 2001-0082059 and 2001-0082060 filed by the present Applicant.
Referring to FIG. 1, in an electrode assembly of a stack/folding type structure 1, a plurality of radical units 1a, 1b, 2, 3 and 4, including a cathode, a separator and an anode stacked in sequence are overlapped, and in each of overlapped parts, a separator sheet 5 is interposed. The separator sheet 5 has a length for wrapping the radical units and is disposed at the overlapped parts of the radical units while wrapping each of the radical units from the radical unit 1a to the outermost radical unit 4 continuously.
The terminal part of the separator sheet 5 is finished by heat welding, by attaching using an adhesive tape 6, or the like. The stack/folding type electrode assembly is manufactured by arranging the radical units 1a, 1b, 2, 3 and 4 on the separator sheet 5 having a long length and rolling the separator sheet 5 from one terminal part thereof one by one. However, in this structure, temperature gradient may be generated between the radical units 1a, 1b and 2 positioned in the center portion and the radical units 3 and 4 positioned at the outer portion, thereby generating different heat emitting efficiencies. Thus, lifetime may decrease after use for a long time.
In general, a separator provided in a radical unit is mainly formed by using a polymer material, and has shrinking properties by heat. An overcharge test and a hot box test are performed with respect to an electrode assembly or a secondary battery including the same to evaluate stability. During performing the tests, some bad electrode assemblies or secondary batteries including the same may ignite. The ignition may be generated because of the shrinkage of the separator due to heat and the short generated through the contact of a cathode and an anode.
Meanwhile, even in a commercial secondary battery after performing the test for stability evaluation, a risk of the shrinkage of a separator due to heat applied from the outside during use or heat generated in the secondary battery, and the generation of short as described above is present.
To prevent the above defects, a separator having a larger size than an electrode may be applied in an electrode assembly.
However, in the electrode assembly of a stack/folding type structure 1, the edge parts of a separator are not attached to an electrode, and a series of manufacturing processes of a secondary battery is conducted without conducting specific treatment with respect to the edge parts of the separator. Thus, there is a high risk of generating short due to overcharge, overheat, etc. In addition, since specific treatment with respect to the edge parts of the separator is not conducted in an electrode assembly of a stack type structure, there also is a high risk of generating short as in the electrode assembly of a stack/folding type structure 1.
Thus, both in the electrode assembly of a stack/folding type structure 1 and the electrode assembly of the stack type, the separator is necessary to have a quite large size when compared to the electrodes to definitely prevent the generation of short between the cathode and the anode. In this case, the volume of the secondary battery may increase.
Here, since the separator is more than necessary, the production cost of a secondary battery may increase.